Anchored Sheet Pile Wall Global Stability
Anchored Sheet Pile Wall Global Stability
(OP)
I am reviewing a failure of an anchored sheet pile wall (14 ft retained ht) along a river where the designer assumed medium dense conditions at the toe of the sheet but let the contractor stop the sheets in very soft clay, 5 to 10 feet above the actual top of the med. dense material. The wall failed in an apparent rotational or global failure with the top of wall moving inward toward shore.
The designer used the SPW911 software but did not consider possible variations in the soil strata or global failure due to consolidation of the soft clay behind the wall due to added fill surcharge and its impact on the stability.
When the fixed earth support method is used, is there a minimum depth of penetration into the medium dense material that is assumed or expected by the software?
The designer used the SPW911 software but did not consider possible variations in the soil strata or global failure due to consolidation of the soft clay behind the wall due to added fill surcharge and its impact on the stability.
When the fixed earth support method is used, is there a minimum depth of penetration into the medium dense material that is assumed or expected by the software?





RE: Anchored Sheet Pile Wall Global Stability
RE: Anchored Sheet Pile Wall Global Stability
http://cedb.asce.org/
RE: Anchored Sheet Pile Wall Global Stability
1. wall designer thinks that the software checks global stability (I don't)
2. designer was CEI on project and did nothing to make sure the tip of the wall was seated into dense material.
RE: Anchored Sheet Pile Wall Global Stability
British Steel Piling Handbook and the US Steel Sheet Piling
Design Manual. I forget if they have a global stability check.
I especially link the statement "Reports on design safety. Unique Rules Of Thumb feature ensures safe designs."
http://www.gtsoft.org/spw911.htm
Manuals link: http://www.gtsoft.org/manuals.htm
RE: Anchored Sheet Pile Wall Global Stability
If the designer stopped the sheets in soft clay 5-10 ft above the sand, this begs two questions 1.) did the designer assume granular material the full depth of the toe? and 2.) was the granular material not at the toe because the sheets were driven short or because the material was deeper than anticipated?
Obviously if the sheets were short, that would contribute to the failure. If the clay ran deeper than anticipated that would have an effect also as the design model for clay is different than granular materials. Most often SPT borings are the most common source of subsurface information which can give very little useful information on clay unless the designer has a lot of experience with the material. Also the propeties of the clay and the resulting load on the wall can change over time.
Finally, there are two design methodoligies for sheeting- Fixed Earth and Free Earth. Free Earth assumes that the sheeting is just long enough for the active and passive pressures and tie loads to balance. Fixed earth assumes that the sheet extends further so that the sheet can develop the cantilever capacity of the sheet, and the tie rod is providingthe required additional reaction to support the sheet. Free earth is statically determinate. Fixed earth is essentally a propped cantilever and is not statically determinate, however can be solved readily by some simplifying assumptions.Free earth has shorter sheets. Fixed earth has longer but lower section sheets and smaller tieback loads. The depth of embedment is important for both methods.
For more details see slideruleeras website for a copy of the US Steel sheetpile design manual.
From your
RE: Anchored Sheet Pile Wall Global Stability
From your post, it would appear global stbility may be an issue. Insufficent embedment may also be an issue which may be due to an unaticippated subsurface profile.
One coment you make is that the designer/CEI did nothing to make sure the tip was seated in dense material. First there is rarely nothing more done in contruction than to be sure the sheet is driven to the specified depth. Second, unlike bearing piles, simply seating the sheets in dense material will not have a significant effect on the capacity of the wall. Changes in profiles can have a radical effect on wall performance.
RE: Anchored Sheet Pile Wall Global Stability
RE: Anchored Sheet Pile Wall Global Stability
The contractor and CEI (original designer) just put the sheets in to the specified depth and never made an attempt to monitor rate of penetration, etc. to confirm they ended up tipped in denser sands below. From there it went downhill and the toe moved outward due to lack of passive resistance/embedment.
Do you think the designer had any responsibility as CEI to make sure the sheets actually penetrated into the materials he assumed were there in his design?
RE: Anchored Sheet Pile Wall Global Stability
jaggith-
To answer your question, I would say typically you would not notice anyting unusual if you are driving with a vibratory hammer, the common way to install sheets. If the sheets are dropping like a rock out of the sky, then yes, you may question the soil. But sands and clays will allow reasonable quick penetration rates. The vibratory hammer does change the insitu conditions during driving, thus unlike impact driving, it is hard to assess subsurface conditions during driving.
However, The entire subsurface profile is very important to design, and the question arises how it could be off so much. Were adequate borings taken or did they guess?(it happens)If the clay was known to exist, it should have been mapped. The whole analysis of the wall would be different for a clay profile than a sand. Also sand does not require as much additional information as clay. It sounds as though the wall did not have adequate
penetration or that the clay could not develop adequate stength for the load imposed, although global stability is still a possibility. The only way to tell is to reanalyze the wall based on the clay profile. Note that when gathering properties for the clay, much of the exposed clay is probably remolded and not indicative of the strength when the system was installed. Best bet is to take borings and recover samples from an area near bu not in the failure.
Notice how no one had time or money to take these borings and tests when it was being design, but now there is plenty of time and the costs, relative to everything else are insgnificant?
RE: Anchored Sheet Pile Wall Global Stability
They also had the ability to review the driven H-pile strut data/blow counts before they installed the sheets and figure out that they missed the boat or that the soils were highly variable in one area. Struts went to 20+ feet below where the sheet piles were arbitarily stopped.
I agree about the cost now versus the minor cost of really exploring it before.
RE: Anchored Sheet Pile Wall Global Stability
Interesting problem
RE: Anchored Sheet Pile Wall Global Stability
Driven length was specified and sheets went to the minimum depth/design length specified.
There was one level of inclined H-pile used as a lateral brace on the water side of wall near top of wall. I referred to that brace as a strut.
RE: Anchored Sheet Pile Wall Global Stability